1 Field of the invention
The present invention relates to a time-division digital switching network wherein incoming digital data channels are isochronous and not necessarily in phase and are switched to outgoing digital data channels. Each digital channel may be a single digital channel, all the data of which are switched to a single outgoing digital channel, or may be a digital component channel of an incoming time-division multiplex digital channel to be switched to at least one of the component digital channels of a number of outgoing time-division mulitplex digital channels.
2 Description of the prior art
As is known, a switching network of the aforementioned kind comprises a receiving and switching part which receives digital data from the incoming channels, wherein each incoming channel corresponds to at least one address of an outgoing digital channel. An intermediate time-division multiplex digital highway transmits words each of which comprises a part conveying data, such as octets or information packets transmitted by the associated incoming channels, and a part relating to the address of the outgoing channel for which the data are intended. A transmission part associates each outgoing digital channel with means for detecting the outgoing channel addresses and means for transmitting the corresponding demultiplexed data from the intermediate multiplex digital highway.
The address of the outgoing digital channel provided in the receiving part is made implicit, for example, if transmission on the intermediate multiplex highway is synchronous, i.e. if the words intended for the outgoing channels are time-division multiplexed in a given order. In the case where the data words have the same format, usually made up of 8 bits or 10 bits, transmission along the intermediate highway is of the conventional PCM kind and the part of each word relating to the address is not transmitted. If, on the contrary, the addresses of the outgoing channels are made explicit, i.e. if each word transmitted on the intermediate multiplex highway comprises both the two aforementioned part, each detection means detects the explicit address of the associated outgoing channel. In that case, transmission on the intermediate multiplex highway may be asynchronous, i.e. the words intended for the outgoing channels are not multiplexed in a predetermined order and the words associated with an outgoing channel are not detected periodically.
In both cases, known switching networks always transmit the implicit or explicit address part of the outgoing channel simultaneously with the part relating to data, which generally contains at least 8 bits.